The United Nations warned Friday of possible war crimes in Ethiopia's Tigray region, as the US condemned the massacre of civilians in fighting which the prime minister claimed had left his enemy "in the final throes of death".
Prime Minister Abiy Ahmed, winner of last year's Nobel Peace Prize, ordered military operations in Tigray last week, shocking the international community which fears the start of a long and bloody civil war.
Hundreds of people are reported to have been killed, some in a gruesome massacre reported by Amnesty International, and thousands have fled fighting and air strikes in Tigray, whose leaders Abiy accuses of seeking to destabilise the country.
The United States urged an immediate de-escalation.
"We condemn the massacre of civilians in Mai-Kadra and strongly urge immediate steps to de-escalate and end conflict throughout the Tigray region," said Tibor Nagy, the top US diplomat for Africa, referring to a town where Amnesty International reported mass killings.
UN rights chief Michelle Bachelet called for a full investigation into the report of mass killings in Mai-Kadra, where Amnesty said it had "digitally verified gruesome photographs and videos of bodies strewn across the town or being carried away on stretchers".
"If confirmed as having been deliberately carried out by a party to the current fighting, these killings of civilians would of course amount to war crimes," she said in a statement.
Amnesty said it had not been able to confirm who was responsible for the killings, however witnesses blamed forces backing the region's ruling party, the Tigray People's Liberation Front (TPLF).
Witnesses also reported the identity cards of some victims indicated they were from the Amhara region, an area with a long history of tensions with Tigrayans, notably over land.
Tigrayan leader Debretsion Gebremichael told AFP on Friday the accusations were "baseless".
Abiy says his military operation was in response to attacks on two federal military camps by the TPLF, which once dominated Ethiopian politics and claims it has been sidelined and targeted under Abiy.
The party denies carrying out the attacks.
- 'Surrounded on all sides' -
On Friday Abiy addressed the region's soldiers, urging them to "rise up" and side with the national army.
"This mischievous force is surrounded on all sides. It is a force in its final throes of death" he said in the Tigrinya language in a speech broadcast on Facebook.
"Rise up against the clique or defect to the Ethiopian defence forces."
A communications blackout in Tigray has made it difficult to verify competing claims on the ground, but Abiy has vowed to deliver a decisive win "in a relatively short period of time".
"This is a daydream," Debretsion said. "We are proud people who can defend ourselves. This is a burial ground for invaders."
Bachelet warned that if the conflict continues "there is a risk this situation will spiral totally out of control, leading to heavy casualties and destruction, as well as mass displacement within Ethiopia itself and across borders".
"I am also extremely alarmed at reports of cuts to essential water and electricity supplies, in addition to the communications blackout and blocking of access by road and air."
- 'Exhausted and scared' -
The UN refugee agency UNHCR said more than 14,500 people have fled into Sudan this week, where aid workers have been overwhelmed.
"People are arriving with very few belongings indicating they fled in a hurry. Arriving children are exhausted and scared," it said.
The agency also warned that fighting was moving closer to a camp in Tigray that houses 6,500 Eritrean refugees.
Alarm is growing over reports of ethnic tensions.
The UN's special adviser on the prevention of genocide Pramila Patten in a statement "condemned reports of targeted attacks against civilians based on their ethnicity or religion".
Ethiopian state media reported that an arrest warrant had been issued for Debretsion and other TPLF leaders, while almost 250 have been arrested in the capital for allegedly conspiring with the TPLF.
A government statement said Friday it had "credible and specific evidence" of TPLF operatives working for local and international organisations.
The statement said police had presented a list of such individuals to the World Food Programme (WFP) in Amhara region, but this was not a "general ethnic profiling".
"We continue to receive credible reports of job suspensions of Tigrayan residents elsewhere in the country as fighting escalates in Tigray," said Laetitia Bader of Human Rights Watch.
"Given the incredibly tense and volatile context in the country, Ethiopian authorities should push back against language and measures that fuel intolerance and risk alienating Tigrayans from all walks of life."